2.0 SHEAR
2.2 Pryout Failure Mode
Variables c ac
Variables ACI 318-19 Chapter 17 Provision Comments for PROFIS Engineering
c ac
17.6.2.6.1 Modification factor for post-installed anchors designed for uncracked concrete in accordance with 17.6.2.5 without supplementary reinforcement to control splitting , ψ cp , N
, shall be determined by ( a ) or ( b ) using the critical distance cac as defined in 17.9.5 .
( a ) If c a , min ≥ c ac
, then ψ cp , N = 1.0 ( 17.6.2.6.1a )
( b ) If c a , min < c ac
, then ψ cp , N = c a , min
c ac
≥
1.5h ef ( 17 . 6 . 2 . 6 . 1b )
17.6.2.6.2 For all other cases , including cast-in anchors , ψ cp , N shall be taken as 1.0 . c ac
17.6 . 2 . 5.1 ……… For anchors located in a region of a concrete member where analysis indicates no cracking at service load levels ……………..
17.9.5 Critical edge distance cac shall be in accordance with Table 17.9.5 unless determined from tension tests in accordance with ACI 355.2 or ACI 355.4 .
Table 17.9.5 – Critical edge distance Post-installed anchor type Torque-controlled Displacement-controlled Screw Undercut
Critical edge distance c ac 4 h ef 4 h ef 4 h ef 2.5 h ef
Example of critical edge distance requirements given in a mechanical anchor approval .
ICC-ES ESR-1917 Table 3
DESIGN |
|
Nominal anchor diameter ( in .) |
|
INFORMATION Symbol Units
|
3 / 8 |
1 / 2 5 / 8 |
3 / 4 |
Effective min . embedment
Min . member thickness
Critical edge distance h ef in . 1-1 / 2 2 2-3 / 4 2 3-1 / 4 3-1 / 8 4 3-1 / 4 3-3 / 4 4-3 / 4 h min in . 3-1 / 4 4 5 5 4 6 6 8 5 6 8 5-1 / 2 6 8 8 c ac in . 6 4-3 / 8 4 4-1 / 8 5-1 / 2 4-1 / 2 7-1 / 2 6 6-1 / 2 8-3 / 4 6-3 / 4 12 10 8 9 ψ cp , N is a modification factor that considers splitting failure for a post-installed anchor when calculating the nominal concrete pryout strength in shear ( V cp or V cpg ). ψ cp , N is only considered when designing post-installed mechanical or adhesive anchors installed in uncracked concrete . Concrete cracks when tensile stresses in the concrete imposed by loads or restraint conditions exceed its tensile strength . ACI 318 anchoring-to-concrete provisions assume cracked concrete as the baseline condition for designing anchors . Uncracked concrete conditions can be assumed if it can be shown that cracking of the concrete at service load levels will not occur over the anchor service life . PROFIS Engineering defaults to cracked concrete conditions .
Splitting failure is influenced by the distance of an anchor from a fixed edge “ in a region of a concrete member where analysis indicates no cracking at service load levels ”. The parameter c ac that is used to calculate ψ cp , N is defined in ACI 318 as the “ critical edge distance required to develop the basic strength as controlled by concrete breakout or bond of a post-installed anchor in tension in uncracked concrete without supplementary reinforcement to control splitting .” Nominal concrete breakout strength in tension ( N cb or N cbg ) and nominal bond strength
( N a or N ag
) are considered when calculating nominal pryout strength in shear . Calculation of these strengths includes the parameter ψ cp , N when uncracked concrete conditions are assumed . Therefore , the parameter c ac is also relevant to pryout calculations when uncracked concrete conditions are assumed .
Testing per the ICC-ES acceptance criteria AC193 and the ACI test standard ACI 355.2 is used to derive c ac values for mechanical anchors . Values derived from this testing are provided in an ICC-ES evaluation report ( ESR ).
Testing per the ICC-ES acceptance criteria AC308 and the ACI test standard ACI 355.4 is used to derive c ac values for adhesive anchor systems . c ac for adhesive anchor systems is calculated using the effective embedment depth ( h ef
), and characteristic bond stress in uncracked concrete ( т k , uncr ).
The c ac
-values for post-installed anchors noted in ACI 318-19 Table 17.9.5 are only intended to be used as “ guide values ” in the absence of c ac values derived from product-specific testing . PROFIS Engineering always uses the c ac
-value that is given ( mechanical anchor ) or calculated ( adhesive anchor system ) in the ICC-ES evaluation report for the anchor .
Reference the Equations and Calculations sections of the PROFIS Engineering report for more information on the parameter ψ cp , N
.
Reference the Variables section of the PROFIS Engineering report for more information on the parameter h ef
.
Reference the Variables section for bond strength in the PROFIS Engineering report for more information on the parameter т k , uncr
.
222 NORTH AMERICAN PROFIS ENGINEERING ANCHORING TO CONCRETE DESIGN GUIDE — ACI 318-19 Provisions